Method for producing low loss nonaging silicon steel sheets



Patented July 25, 1933 UNITED STATES PATENT OFFICE w-ns'rox 303mm orrrr'rsrrmn, uassacnusn'r'rs, assrenon '10 GENERAL nLr-c'rme company, Aconroaa'rron' or mew Yoax METHOD FOR PRODUCING LOW- LOSS NONAGINGSILICON STEEL SHEETS ll'o Drawing.

The present invention relates to magnetic material and more particularlyto a method for producing low loss silicon steel which does not age.

If silicon steel sheets are subjected to a single sheet anneal, i. e. ananneal in which spaced sheets are passed through an annealing furnace,as disclosed for example in Ruder Patent No.1,156,496, the resultingproduct has a low total watt loss when employed as core material foralternating current transformers and the like. The annealed sheetshowever do not retain their high magnetic qualities indefinitely. Theyhave a tendency to age causing thereby an increase in the total wattloss of the material which may vary from about 30 to 60%.

It is an object of the present invention to provide a method for heattreating silicon steel sheets whereby low watt losses may be obtainedparticularly at high magnetic densities. A further object of theinvention is to produce magnetic sheets which do not age and therebycause an increase in the watt losses in the material.

In accordance with the present invention silicon steel sheets which maycontain up to about 7% silicon and which have been pickled are placedin'a furnace the atmosphere of which is hydrogen andheated to atemperature of 700 C to 850 0., preferably 800 C. The sheets areannealed at this temperature for about five minutes and then removed andcooled either by quenching or rapid air cooling, preferably the latter.If the sheets are quenched it is desirable to quench them in a picklingsolution. When cold, the single sheets may. be punched, sheared or cutinto desired shapes and a ain placed in a furnace the atmosphere of wich is hydrogen and annealed at a temperature above 850 C., for example900 C. to 1100 C. but preferably 925 C. The sheets are maintained atthis temperature for about five minutes and then removed and withoutquenching, cooled rapidly in air to room tem erature. Although ininitiating my process I prefer to employ sheet.material which has beenpickled the process may be carried out with 1932. Serial in. 586,158.

unpickled material if desired. I have also found that some'advantage maybe obtained by pickling the sheets after the first anneal. A furtherimproved magnetic quality results therefrom as well as greateradaptability to a straight line process. I prefer to employ a picklingbath consisting of a 10% sulphuric acid solution held at a temperatureof about 90 C. My invention however is not limited to this particularbath since othe' pickling baths may be employed if desire v I have foundit advantageous to shear or punch the sheets after they have been giventheir first anneal. Under such circumstances the annealed sheets areusually air cooled, pickled, punched and then annealed at a temperatureof about 925 C. The second anneal removes all traces of cutting strainand leaves the punchings ready for use. i

While I prefer to employ a hydrogen atmosphere in the annealing furnace,the invention is not limited to the use of any particular atmosphere.Any other ordinary furnace atmosphere such as air, nitrogen,hydrogen-nitrogen mixtures or a vacuum may be employedif desired.Furthermore, although the period of time that the sheet material ismaintained in the furnace is usually about five minutes this period oftime is not critical. It is chosen in the interest of economy and may belonger or shorter if desired without adversely affecting the sheetmaterial. It is merely neeessary that the sheets'should reach thedesired temperature and this can usually be accomplished in about fiveminutes.

The present process may be adapted easily to any straight linecontinuous process for treating magnetic sheet material. Moreover, whenmagnetic sheet material is.

treated in accordance with the present invention it is possible toeffect an appreciable reduction in total watt losses at high magneticdensities. For example at 15000 B the reduction in total watt losses mayamount to 15 or 25%. Furthermore, the heat treated material does notage.

What I claim as new and desire to secooling said sheets, heating thesheet ma terial to e temperature hetween 850 C. and 1100 C. and quicklycooling the sheet ma,- teriel,

2. The method of treatingsilicon steel sheet material which comprisesheating sin le steel sheets for a, few minutes in a hydrogen atmosphereand at a, temperature beween 700 C. and 850 (1, quickly cooling thesheets, heating the sheet material to a temperature between 850 C. and1100 (l, and quickly cooling the sheet material in air withoutquenching.

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single sheets at a, temperature between 700 C. and 850 (1., quicklycooling said sheets, pickling the sheets, punching or cutting saidsheets into desired shapes, heating the single punchings to atemperature between 850 C. and 1100 C., and quickly cooling thepunchings without quenching.

WESTUN MURR LL.

